A problem in exploiting the vast potential of the wireless Internet is that the wireless medium is prone to errors, rendering it unreliable for data. This has not impeded the widespread adoption of cellular services, because the voice application is not as sensitive to the vagaries of the radio frequency (RF) environment. As a result, cellular technologies have been optimized over the years for the voice application and its error threshold.
Data requirements dramatically differ from voice. As compared with wireless voice, data require several orders of magnitude improvement in error rates. This has not impeded the mass adoption of Internet access because the Internet itself was designed around the highly reliable connections available in present wired networks.
Delivering Internet services poses some unique challenges for the wireless industry. Cellular technologies are circuit-oriented and voice-optimized, resulting in low practical throughput and high latency for data applications. Latency is the time, represented in seconds (s), required to transfer a message between relevant devices in the network. Latency is the sum total of the delay introduced by the sender software, the delay introduced by the receiver software, the delay in accessing the network, the delay introduced by the network. Latency affects the transfer time of a message according to the following equation: message transfer time=latency+((length of message)/(data transfer rate)). Data transfer rate, represented by bits per second (bits/sec), is the speed at which data can be transferred between the sender and the receiver in a network, after transmission has begun. Length of a message is amount of information, represented by the number of bits, in the message.
For example, in present wireless network standards (e.g., 1×RTT, 3GPP, HDR) that employ medium access control (MAC) protocol designs, a mobile station includes three states, a null state, an idle or dormant state, and an active state. In the active state, communication resources are allocated to the mobile station and data bursts pass instantly between the network and the mobile station. However, much of the communication resource allocated is not used due to the bursty nature of data traffic. Accordingly, mobile stations that are not actively transmitting data are moved from the active state to the idle state when data traffic has not occurred for a period of time. Then, if data traffic needs to be sent between the idle mobile station and the network, the mobile station needs to move from the idle state to active state before the data can be transferred. Typically, the delay introduced for moving the mobile station from the idle state to the active state is one to five seconds for each of the three wireless network standards, regardless of the Quality of Service (QoS) provided to the mobile station, as shown in FIG. 10. Such a long packet access delay does not meet the requirement for a mobile station to be “always on”. Moreover, in the present wireless network standards, the QoS is predetermined and fixed or static, according to system engineering design considerations. Hence, in addition to the packet access delay, the fixed QoS may cause the mobile station to perform at a substandard level (e.g., additional delays and/or increased power consumption).
These problems have been addressed using several approaches. In a first approach, the network modifies the information content to fit the channel bandwidth (i.e., the “pipe”). Second and third generation (2G and 3G) cellular solutions incrementally add data capabilities to their hierarchical, voice-centric networks. In this approach, the application is re-defined around the existing wireless “pipe” by rewriting/thinning down the content and avoiding interactive applications, such as voice-over-IP (VoIP). This not only limits the user experience to a mere fraction of what's possible on the Internet but also comes at a hefty price premium because the immense content, applications and infrastructure of the Internet are not leveraged, but re-invented.
In a second approach the mobility of the mobile station is limited to increase data throughput. Some approaches address only one cause of data errors in a wireless environment—mobility. In this case, mobility is either prevented by employing fixed directional subscriber antennas, or by reduced by providing spot coverage and/or no handoff from cell-to-cell. These approaches either add significant cost and complexity (fixed user antennas, installation required) or limit the system's utility and revenue potential (limited coverage, no fully mobile applications).
In a third approach the network and/or the mobile station tunes the radio link to increase throughput over the communication channel. The wireless environment, more often than not, disrupts radio signals, resulting in transmission errors. Some wireless technologies attempt to repair the temporal characteristics (e.g., through equalizers) or spatial properties (e.g., though smart antennas) of the radio signals in real time. The result is a performance gain, but a proportional increase in system complexity. While these approaches can be applied to any air interface, they add significant cost and complexity.
Despite these limitations, network operators continue to move forward with plans to market mobile broadband data to enterprises and consumers because of the mass-market demand for mobile broadband services and the potential for profits. Ideally, a network should offer users a wireless broadband experience that has the same look and feel of wired broadband, with access to all existing web sites and applications. Practically, a network should realize profitable economics for the operator and a positive experience for the end user by meeting the following network characteristics. A network should support all existing wire line applications, with no changes to applications, devices, protocols, and content. A network should achieve significant profitability for operators and manufacturers in a high usage, flat-rate environment. A network should deliver high spectral efficiency with ability to activate a large pool of mobile users. A network should be designed to be packet-switched, and leverage existing standard-based architectures. A network should have minimal latency (less than 100 ms) to support interactive applications. A network should support transparent access between wireless local area network (LAN) and wireless wide area network (WAN). A network should support subscriber identification and differentiation through industry standard data policies. A network should support toll-quality packet voice applications and “instant connect” services. A network should support multicast for bandwidth efficiency, and streaming applications. A network should provide high, end-to-end security for web-based financial transactions. A network should support end-to-end Internet protocol (IP) Quality of Service (QoS), wherein QoS is typically represented by metrics that affect the quality of a data service that is delivered to the mobile station (e.g., throughput, bit error rate (BER), delay, etc.).
In a mobile station, the QoS affects the power consumption, otherwise known as battery life, which directly affects the duration of time that the mobile station can operate before the battery needs to be recharged or replaced. It would be desirable for the mobile station to support multiple levels of QoS support to permit various compromises between QoS and power consumption, depending on various factors, such as the quality of the channel, the type of data service, etcetera. For example, some users might desire “instant access” without caring about the power consumption (e.g., in fixed wireless access environment). Other users might desire efficient power consumption, while tolerating longer packet access delay.
Today's predominant mobile technologies, namely second and third generation cellular technologies, were conceived and designed before the birth of the World Wide Web and the explosion of the Internet. These technologies were optimized for voice applications and do not effectively meet the present and anticipated mass-market demand for mobile broadband services. Accordingly, there is a need for a medium access control (MAC) protocol for a wireless communication system that overcomes the disadvantages mentioned above.